1 Field of the Invention
The present invention relates to an apparatus for and a method of Hough-converting coordinate data.
2. Description of the Related Art
As one of methods for detecting straight line segments, there is known one referred to as "Hough Conversion" (disclosed in U.S. Pat. No. 3,069,654, for example). Hardware for effecting the Hough conversion is disclosed, for example, in the article "Hardware for Hough Conversion Using ROM" by K. Onda, et al., (all-Japan meeting of the 70th anniversary of the founding of the Institute of Electronics and Communication Engineers of Japan, No. 1587, 1987). The disclosed is shown in FIGS. 1 and 2.
FIG. 1 is a block diagram of a single processing element PE. FIG. 2 is a block diagram showing a Hough converting circuit having k+1 processing elements PE.sub.0 to PE.sub.k obtained by dividing .rho.-.theta. parameter space into k+1 pieces in a .theta. direction and connected in parallel. As shown in FIG. 1 , the processing element PE comprises memories ROM1, ROM2 for storing therein values of data of x.multidot.cos.theta..sub.n and y.multidot.sin.theta..sub.n, respectively, for each value .theta., taking x, y as addresses, flip-flops FF1, FF2 for temporarily storing therein the values of the data of x.multidot.cos.theta..sub.n and y.multidot.sin.theta..sub.n, which are outputted from the ROM1, ROM2, respectively, and an adder (ADD) for adding the values of the data of x.multidot.cos.theta..sub.n and y.multidot.sin.theta..sub.n so as to output the added result of Hough conversion, i.e., .rho. by the following equation: EQU .rho.=x.multidot.cos.theta..sub.n +y.multidot.sin.theta..sub.n
According to the processing element PE, the expressions (x.multidot.cos.theta..sub.n and y.multidot.sin.theta..sub.n) representing a Hough curve (sine curve) in a .rho.- .theta. plane can be added as given below if the values of coordinates (x, y) in an X-Y rectangular coordinate system are inputted. EQU .rho.=x.multidot.cos.theta..sub.n +y.multidot.sin.theta..sub.n
Therefore, k+1 kinds of values .rho. (.rho..sub.0 .rho..sub.1, . . . , .rho..sub.k) with respect to the coordinates (x, y) can be determined simultaneously by connecting the k+1 processing elements in parallel as shown in FIG. 2.
However, this method has a disadvantage that the ROM1 and ROM2 must be provided for each value .rho.. It is therefore difficult to integrate easily the components of the Hough converting circuit into LSI chips, so that hardware is significantly large-scaled and complicated. In order to facilitate the integration of the components into the LSI chips, there is known a method for making ROMs in the form of RAMs. However, such a method has a disadvantage that the degree of integration cannot be increased. In addition, the resolution capabilities of the Hough converting circuit in a .theta. direction in the .rho.- .theta. parameter space are determined by the data stored in the ROM1 and ROM2. It is therefore very difficult to carry out a change in setting of the resolution of the circuit in the .theta. direction.